1. Field of the Invention
This invention relates generally to an exercise machine for performing isolation exercises, and is particularly concerned with an arm exercise machine with a self-aligning pivoting user support.
2. Related Art
Two most commonly performed arm exercises are the biceps curl and triceps extension. These are isolation exercises, so-called because they involve a single joint, the elbow; require the movement of just one body part, the lower arm; and target a specific muscle group, biceps (curl) and triceps (extension). Because only one joint action is involved, isolation exercise machines use exercise arms with rotational movement that align the pivoting joint of the user with the pivot axis of the arm. It is important that the user is properly positioned when performing these exercises, in order to reduce joint stress and reduce the risk of injury.
There are three major sticking points or hurdles that a user must overcome in order to perform a biceps curl. The first is in the beginning of the exercise, where starting off with the arms fully extended places the elbows in a bio-mechanically weak position and makes it difficult to initiate the curling motion under load. The second is breaking through the gravitational apex of the movement where the elbow is bent at 90 degrees. The final hurdle is achieving full flexion and properly completing the exercise. When performing the exercise with free weights (barbell or dumbbells) users often overcome these sticking points by performing what is often called “cheat” curls. This requires the user to bend their knees slightly, lean forward at the waist and then explode the weight up by thrusting with the legs, swinging the arms and arching the back rearward. This uses momentum to bring the weight to the top of its arc and complete the exercise. While it is considered one of the best ways to increase muscle mass because it allows the user to handle more weight than normally possible with stricter form, it can be harmful to the low back. This version of a biceps curl also involves other body parts as well as inertia to complete the movement, and does not focus strictly on the biceps. To help maintain a stricter form, most biceps curl machines place the user in a fixed seated position with their arms positioned against a pad. While this prevents the user from involving their legs, back and shoulders in the exercise, focusing strictly on their biceps, it can put too much stress on the elbow.
In order to achieve the full exercise range-of-motion, there must be enough pre-stretch at the beginning of the exercise, but too much forces the elbow to hyper-extend under load. Equally important is achieving full flexion to the elbow and completing the exercise. If the resistance is too heavy at the end of the movement, the user will stop short, barely passing the apex; if the resistance is too light there could be a “caming over” effect, where it feels as if the speed at which the handles are moving increases after they pass the gravitational apex.
The same problem points exist for the user performing a triceps extension as on a biceps curl. The beginning of the exercise places the user's hands in close to their body with the elbow bent. This again is a bio-mechanically weak position and makes it difficult to initiate the pushing motion under load. Next is breaking through the gravitational apex of the movement where the elbow is bent at ninety degrees. The final problem point is achieving full extension and properly completing the exercise.
When performing the triceps extension exercise with free weights (barbell or dumbbells) the user is either standing or lying on their back. They start with their upper arms extended outward, elbows bent and hands at head level. They then straighten their arms, moving only at the elbow. The same “cheat” method of swinging or throwing the weights upward to create momentum and involve other muscle groups (shoulders and/or back) is also used during this exercise.
To maintain a strict form, most triceps extension machines place the user in a fixed seated position, arms positioned against a pad, often with their back supported to help brace against the outward push on the exercise arm. In order to achieve the full exercise range-of-motion, there must be enough pre-load at the beginning of the exercise, but too much makes it difficult to unfold a bent arm under load. Equally important is achieving full extension to the elbow and completing the exercise. If the resistance is too heavy at the end of the movement then the user will stop short, barely passing the apex; if the resistance is too light there could be a “caming over” effect, where it feels as if the speed at which the handles are moving increases after they past the gravitational apex.
In attempting to overcome or reduce the problem points discussed above, prior art biceps and triceps exercise machines have used various angles for the arm support pad, added counter-balancing weight to the exercise arm and installed devices to alter the resistance curve during various stages of the exercise movement.